1. Field of the Invention
This invention relates to a method and apparatus for marking the surface of an object, and more particularly, to a method and apparatus for imprinting a preselected array of characters in the circumference of an arcuate object.
2. Description of the Prior Art
Dot matrix marking devices that utilize individual marking pins to imprint alphanumeric characters in the generally flat surface of a workpiece are well known.
British Pat. No. 2,002,694 discloses a programmable dot matrix type of engraver for impressing a selected size of alphanumeric characters in a workpiece. The engraver is computer controlled to provide selective continuous marking of the workpiece to overcome the delays encountered with manual engravers. An engraving tool is supported on an arm which is movable on a carriage by a leadscrew rotated by a stepping motor. The carriage is movably mounted on a horizontal arm that is, in turn, supported by a vertical column above a base on which the workpiece to be marked is stationarily positioned. With this arrangement, the engraving tool is movable along horizontal X and Y axes. The engraving tool includes a punch which is remotely controlled by a central processing unit through a solenoid operated air valve to form the desired dot matrix character whereby the size of the figure engraved is determined by the number of stepping motor steps between each point of the 7.times.5 matrix. Furthermore, similar to the wire dot matrix printers for computers, there is now also available an engraver with marking pins selectively actuated and arranged in a straight line configuration which can form alphanumeric characters by collectively traversing a given number of lateral units.
U.S. Pat. No. 4,506,999 discloses pneumatically controlled apparatus that includes an array of pins utilized to emboss alphanumeric characters in a workpiece. Seven pins move across the workpiece and selectively mark the workpiece with the desired characters. The angular arrangement of the pins determines the height of the characters and rotation of the head adjusts the angle of the line of pins. The angular adjustment is made manually by means of ball lock pins.
U.S. Pat. No. 4,591,279 discloses a marking head assembly that is pivotally mounted on a plate and carries a plurality of impact pins which are reciprocated into and out of contact with the relatively flat surface of a workpiece by operation of programmable solenoid valves. An indexing wheel adjusts the angular position of the marking head assembly to control the size of the characters formed by the pins impacting the workpiece. A ballscrew drive connects the plate to a frame for imparting longitudinal movement of the plate as the marking head assembly imprints a plurality of marks in the surface of the workpiece.
While it has been suggested by the prior art devices to utilize individual marking pins reciprocated into and out of contact with the surface of a workpiece to form a dot matrix array of alphanumeric characters, these devices are limited in that they will only imprint a dot matrix array in a relatively flat workpiece. There is a need for an improved dot matrix marking device that is computer controlled to rapidly mark the circumference of an arcuate object with a dot matrix array of alpha or numeric characters and also a combination of alphanumeric characters. The dot matrix marking device must be adaptable for marking the circumference of arcuate objects of varying diameters.